Mechanical properties of EPS lightweight concrete

Construction Materials Volume 164 Issue CM4 Mechanical properties of EPS lightweight concrete Chen and Fang

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Proceedings of the Institution of Civil Engineers Construction Materials 164 August 2011 Issue CM4 Pages 173–180 doi: 10.1680/coma.900059 Paper 900059 Received 23/11/2009 Accepted 25/03/2010 Published online 07/06/2011 Keywords: concrete technology & manufacture/strength and testing of materials ICE Publishing: All rights reserved

Mechanical properties of EPS lightweight concrete 1 &

Bing Chen MEng, PhD Department of Civil Engineering, Shanghai Jiaotong University, Shanghai, P. R. China

2 &

Congqi Fang MEng, PhD Department of Civil Engineering, Shanghai Jiaotong University, Shanghai, P. R. China

The aim of this study was to investigate the effects of expanded polystyrene aggregate size, matrix strength and polypropylene fibre addition on the strength of lightweight concrete. Three types of expanded polystyrene beads with 1?0, 2?5 and 6?3 mm diameter were added to a high-strength matrix to produce lightweight concrete. Fine silica fume and polypropylene fibres were used to improve material properties. Lightweight expanded polystyrene concretes with different matrix strengths were investigated for compressive and splitting tensile strength. The expanded polystyrene concrete with small expanded polystyrene beads showed higher compressive strengths and the increase was more pronounced in lowdensity concrete than high-density concrete. The matrix strength was also observed to affect the particle size effect of expanded polystyrene beads on the compressive strength of concrete. The increase in compressive strength with the decrease of expanded polystyrene bead size was more pronounced in the low-strength matrix. In addition, polypropylene fibres significantly improved the strength of expanded polystyrene concrete, with the 28-day compressive and splitting tensile strengths of expanded polystyrene concrete being up to 43 and 44% higher than those of reference concrete.

1.

Introduction

With the recent rapid developments of high-rise buildings, larger and longer spanning concrete structures, better concrete performance with higher strength, lower density, higher toughness and other properties is urgently required. In recent years, lightweight concrete has been used for structural purposes to meet these requirements (Narayanan and Ramamurthy, 2000). Among the various types of lightweight concretes that have been proposed, those obtained by mixing high-performance paste with millimetre-size expanded polystyrene (EPS) are particularly interesting for their excellent properties, such as the ability to be fabricated on the construction site, the tailoring of properties by varying material parameters, and good energy-absorbing characteristics (Babu et al., 2006; Bischoff, 1990; Cook, 1983). Polystyrene concrete is a mixture consisting of cement, sand and polystyrene aggregate. The research on EPS concrete can be traced back to 1973 when Cook investigated EPS as the aggregate of concrete (Cook, 1973). In recent years, much research has focused on EPS concrete, including experimental and theoretical research (Babu and Babu, 2003; Babu et al., 2005; Chen and Liu, 2004, 2007; Chen and Fang, 2009). It has been shown that the mechanical properties of EPS concrete can be significantly improved with the addition of steel fibres, silica fume, fly ash or bonding additives to the concrete matrix.

Previous research indicates that the compressive strength of EPS lightweight concrete increases with a decrease in EPS bead

size, for the same concrete density (Miled et al., 2004, 2007; Roy et al., 2005). This scaling phenomenon was first observed by Roy et al. (2005) on the basis of an experimental investigation aiming to formulate and optimise an EPS concrete with a density ranging from 600 to 1400 kg/m3 and possessing structural strength with more than 20 MPa. Later, this phenomenon was confirmed by Ganesh Babu (Babu et al., 2006). Recently, Miled and Roy (Miled et al., 2004, 2007; Roy et al., 2005) carried out research on this phenomenon and developed a mathematical model to predict strength. In the present study, three sizes of polystyrene beads were used with differing strengths of mortar matrix. The main objective of this work was to determine the effect of polystyrene aggregate size and matrix strength on the strength of EPS concrete. Furthermore, the effect of polypropylene (PP) fibres on the strength of EPS concrete was also studied.

2.

Experimental details

2.1

Materials and mix proportions

ASTM Type I ordinary Portland cement (OPC) with 28 days compressive strength of 72?5 MPa was used for all concrete mixtures. The chemical composition of the cement used is given in Table 1. The silica fume used was a dry uncompacted powder from Elken Materials with SiO2 content of 92?4%. The amount retained on a 45 mm sieve was 1?6%. The detailed chemical composition is given in Table 1. Fine aggregates with special gradation were selected for the concrete, as shown in Table 2. Polypropylene fibre with a length of 10 mm and diameter of 173

Construction Materials Volume 164 Issue CM4

Mechanical properties of EPS lightweight concrete Chen and Fang

100 mm was used; its properties are shown in Table 3. Three types of commercially available spherical EPS beads that are essentially single sized (types A, B and C) were selected. The grading and densities of the three EPS bead types are given in Table 2. In the present study type A replaced fine aggregates and types B and C replaced coarse aggregates, respectively. A naphthalene-based superplasticiser was used to produce highly flowable mixes to suit the hand compaction adopted. In this research, three basic matrixes with strengths of 130, 90 and 50 MPa were prepared, and the complete details of the basic matrixes are presented in Table 4. For compressive strength testing the matrix was made from mortar without EPS addition and it was cured in a fog room (95 ¡ 3%; relative humidity, 22 ¡ 2˚C) for 28 days. Cubes of 100 mm size were used for testing and the results from three specimens were used to evaluate the average value.

2?5 kN/s. The splitting tensile strength test was conducted on cubes at 28 days according to ASTM C 496-89 (ASTM, 1989). The absorption test was carried out in accordance with ASTM C 642-82 (ASTM, 1982). Each of the reported results for the compressive strength and splitting tensile strength is an average of three specimens. However, if the variation between the maximum (or minimum) and mean values was more than 15%, an additional specimen was tested to find the average.

2.2

Mixing of EPS concrete

The concrete was mixed in a planetary mixer of 30 l capacity. Water, superplasticiser, silica fume, sand and cement were successively introduced into the mixer. After 5 min of mixing, when the matrix became homogeneous, polystyrene beads were introduced and the mixing was continued until a uniform and flowing mixture was obtained. The fresh concrete densities were measured immediately after mixing, and the fresh concrete poured into moulds and compacted by hand.

2.3

Casting, curing and testing of concrete specimens

Cubes of 100 mm size were used for measuring the compressive strength at 3, 7, 14, 28 and 60 days, and also for the splitting tensile strength test at 28 days. Each batch produced 21 cubic specimens of 100 mm size. The specimens were demoulded approximately 24 h after casting and placed in a fog room (95 ¡ 3%; relative humidity, 22 ¡ 2 ˚C). Compressive strength tests were carried out in a testing machine of 2000 kN capacity at a loading rate of

Silicon dioxide (SiO2) Aluminium oxide (Al2O3) Ferric oxide (Fe2O3) Calcium oxide (CaO) Magnesium oxide (MgO) Sodium oxide (Na2O) Potassium oxide (K2O) Sulfur trioxide (SO3) Loss on ignition

OPC

Condensed silica fume

21?60 4?13 4?57 64?44 1?06 0?11 0?56 1?74 0?76

92?40 0?80 0?50 0?91 0?27 – – – 2?00

Table 1. Chemical composition of cementitious materials

174

3.

Results and discussion

3.1

Compressive strength

3.1.1 Effect of age The variation of compressive strength with age for different size polystyrene aggregates is shown in Figure 1. It can be observed that for similar concrete densities, the strength of concrete increased with a decrease in the size of EPS aggregate and this was in accordance with recent studies (Babu et al., 2006; Cook, 1983). This increase was consistent for all concrete densities (1000, 1400 and 1800 kg/m3). It was also found that the compressive strength of EPS concrete in almost all mixes displayed a continuous increase with age. The rate of strength development was greater initially and decreased as the age increased, with matrix strength having a direct effect on it. For EPS concrete with similar densities, the 1 day strength was about 50 to 55% of the 28 day strength for a 130 MPa strength concrete, whereas it was only about 35 to 40% for 50 MPa concretes. From the mix proportions, the main difference between the 130 and 50 MPa strength concretes was the silica fume content, which was 30% for the former and only 10% for the latter. This indicates that the rate of strength gained with age for EPS concrete containing silica fume increased with an increase in the silica fume percentage. This might be partly due to the high heat of hydration in the matrix containing high percentages of silica fume, therefore gaining high strength at an early age (Babu and Babu, 2003). Comparison of the strength at 28 and 60 days indicated that at later ages all mixes showed no appreciable improvement in compressive strength. 3.1.2 Effect of density and EPS volume fraction Density is one of the important parameters which can control many physical properties in EPS concrete and it is mainly controlled by the volume fraction of polystyrene aggregate. The compressive strengths of EPS concretes with different plastic densities and EPS volume fractions are presented in Figure 2. The plastic density of normal concrete with a compressive strength of 130 MPa was 2258 kg/m3. Considering the EPS concrete with 1 mm polystyrene aggregate size and 130 MPa matrix strength, its plastic density was about 80, 60 and 45% of that of normal concrete, when its strength was about 46, 24 and 10% of normal concrete, respectively. For a normal 50 MPa strength matrix with 1 mm polystyrene aggregate size, at EPS concrete plastic density of about 80, 60 and 45% of normal concrete, the strength was



Grading of aggregate cumulative passing (%) Polystyrene aggregate Sieve size 9?5 mm 4?75 mm 2?36 mm 1?18 mm 600 mm 300 mm 150 mm Density: kg/m3

Fine aggregate

Type A

Type B

Type C

100 100 100 83 55 30 3 2500

100 100 100 100 0 0 0 33

100 100 100 0 0 0 0 19

100 100 0 0 0 0 0 17

Table 2. The gradation and densities of aggregates

Length: mm 10

Diameter: mm

Density: kg/m3

Modulus: GPa

Elongation at break: %

Tensile strength: MPa

100

900

8

8?1

800

Table 3. Properties of PP fibre

only about 45, 19 and 8% of normal concrete, respectively. This indicates that the decrease in compressive strength with a decrease in plastic density was significant in a high-strength matrix when the plastic density was low. This might be due to the fact that EPS concrete with a low-strength matrix and a low plastic density had high quantities of EPS, inherently had lower strength and therefore the benefit obtained with the use of the high-strength matrix was significant. 3.1.3 Effect of polystyrene aggregate size and matrix strength Figure 3 illustrates the effects of polystyrene aggregate size on the compressive strength of EPS concrete with different plastic densities. It was noted that the particle size effect of EPS beads differed as the plastic densities and matrix strengths changed. For EPS concrete with a plastic density of 1800 kg/m3 and

Matrix strength: MPa

w/c

130 90 50

0?2 0?25 0?3

matrix strength of 130 MPa, there was a compressive strength increase of 22% with 1 mm EPS beads in comparison with 2?5 mm EPS beads, and an increase of 17% with 2?5 mm EPS beads in comparison with 6?3 mm EPS beads. However, when the plastic density was 1400 kg/m3, increases of 36 and 22% were observed, respectively, for 2?5 and 6?3 mm EPS beads. This indicates that the size effect of EPS beads became more pronounced with the increase in EPS volume fraction. This might be due to the fact that lower density concrete generally has a high volume fraction of EPS, inherently having lower strength, therefore the benefit obtained with the use of small size aggregate was significant. It was also observed that, for EPS concrete with the same plastic density, the particle size effect of EPS beads became slightly lower with the decrease in matrix strength. The main reason for this is believed to be that in EPS concretes of similar plastic densities the strength

Water: kg/m3 Cement: kg/m3 246 295 339

861 944 1017

Silica fume: kg/m3

Sand: kg/m3

Superplasticiser: ml/kg of cementitious materials

369 236 113

768 737 706

1?2 1?0 0?8

Table 4. Basic mix composition of the different strength matrixes

175



70

1 mm 2.5 mm

1 mm 2.5 mm

6.3 mm

6.3 mm

60

20 1800 Compressive strength: MPa

Compressive strength: MPa

1800 50

40

30 1400

15

10 1400

20 5 10

1000

1000

0

0 0

10

20

30

40

50

60

70

80

0

10

20

30

40

Age: days

Age: days

(a)

(b)

50

60

70

80

Figure 1. Variation of compressive strength with age for different densities at different matrix strengths (a) matrix strength at 130 MPa; (b) matrix strength at 50 MPa

140

140

1 mm 2.5 mm

1 mm 2.5 mm

6.3 mm

120

6.3 mm

120

Matrix with strength of 130 MPa

100

80 Matrix with strength of 90 MPa 60


40

100

80 Matrix with strength of 90 MPa 60 Matrix with strength of 50 MPa 40

20

20

0 0

10

20

30

40

50

60

0 800

1000 1200 1400 1600 1800 2000 2200 2400

EPS volume fraction: %

Plastic density: kg/m3

(a)

(b)

Figure 2. Variation of compressive strength with density and EPS volume

176






70

1 mm 2.5 mm 6.3 mm

130 MPa

60

90 MPa

50 40

130 MPa

30 50 MPa

20

90 MPa

130 MPa

50 MPa

10

90 MPa 50 MPa

0

1800

1400 Plastic density: kg/m3

contribution due to the use of small size beads is less in higher strength matrixes. To make the comparison between the compressive strengths of the three EPS bead size concretes easier, for the same plastic density, the compressive strengths were normalised, given by the ratio sEPS/smatrix, where sEPS is the compressive strength of EPS concrete at a given plastic density and EPS bead size, and smatrix is the matrix strength. Figure 4 shows the effect of matrix strength on the normalised compressive strength of EPS concrete with different plastic densities. It can be seen that, for a given plastic density and EPS bead size, the normalised compressive strength increased with the increase in matrix strength. It is thus evident that a high-strength matrix has to be used to produce high-strength lightweight concrete. 3.1.4 Effect of PP fibre Figure 5 presents the effect of PP fibre on the compressive strength of EPS concrete with a matrix strength of 130 MPa. It 0.50 0.45 0.40 0.35

1 mm

Matrix with 130 MPa Matrix with 90 MPa Matrix with 50 MPa

2.5 mm 6.3 mm

0.30 0.25

1 mm 2.5 mm

0.20 0.15

6.3 mm 1 mm 2.5 mm

0.10 0.05 0

6.3 mm

1800


1000

Figure 4. Normalised compressive strengths obtained with different strength matrixes and EPS bead sizes

60

1 mm 8%

2.5 mm 6.3 mm 20%

Without PP fibre With PP fibre

24%

50 1 mm 2.5 mm 6.3 mm

40

12%

30

1 mm 2.5 mm 6.3 mm 18%

20

22% 25%

10 0

1000

Figure 3. Effect of EPS bead size on the compressive strength of EPS concrete in different densities and strength matrixes

Normalised compressive strength: MPa

70 Compressive strength: MPa


20

38.6 EPS volume fraction: %

24%

23%

56.5

Figure 5. Effect of PP fibre on the compressive strength of EPS concrete with matrix of 130 MPa

was found that PP fibres could greatly improve the strength with the highest increase being 25% in comparison with the corresponding EPS concrete without PP fibres. At low EPS volume fraction, the increase in compressive strength by the addition of polypropylene fibres was greater for increased EPS bead sizes. On the other hand, when the EPS volume fraction was high, the particle size effect of EPS beads on strength with increasing PP fibre content became negligible. It was also noticed that, for a given EPS beads size, the effect of PP fibre on compressive strength became more noticeable as EPS volume fraction increased. Figures 6 and 7 show the effects of PP fibres on the compressive strength of EPS concrete with matrix strengths of 90 and 50 MPa, respectively. Similar phenomena were observed as for the EPS concrete with matrix strength of 130 MPa. Polypropylene fibres can increase the compressive strength greatly. From the results presented in Figures 5, 6 and 7, it was found that, for a given EPS bead size and volume fraction, the increase in strength by PP fibre addition decreased with increasing matrix strengths. For lightweight concrete with 1?0 mm EPS beads and 1800 kg/m3 plastic density, for example, the compressive strength of the sample with 130 MPa matrix strength increased by only 8%, whereas for the samples with 90 and 50 MPa matrices, the strength increases were 20 and 21%, respectively. This indicates that, for EPS concrete with low matrix strength, adding PP fibre is effective in improving the strength.

3.2

Splitting tensile strength

Similar to compressive strength, the splitting tensile strength of EPS concrete also decreased with increasing EPS volume content. The variation of splitting tensile strength (ft) plotted against compressive strength is presented in Figure 8. It can be observed that the splitting tensile strength increased with increasing compressive strengths. Previous research studies 177



50 40

1 mm

With PP fibre

20% 17%

22% 1 mm

30

2.5 mm 6.3 mm

22%

20

1 mm 20%

2.5 mm 6.3 mm

23% 22%

10

24%

0

19.4

7

Without PP fibre

2.5 mm 6.3 mm


20%

55.8

have indicated that the relationship between splitting tensile strength and compressive strength can be expressed as: ft ~a|fcyb (where fcy is the compressive strength). For example, in the literature (Babu et al., 2005), the relationships between splitting tensile strength and compressive strength of EPS : : concrete were ft ~0:23|fcy0 67 and ft ~0:358|fcy0 6557 . In the present study, the proposed equation (r 5 0?98) based on the results of EPS concrete tests is given as : ft ~0:3826|f 0 6557

Figures 9 and 10 display the effect of PP fibres on the splitting tensile strength of EPS concrete with a matrix strength of 130 MPa and 50 MPa, respectively. It can be seen that PP fibres increased the splitting tensile strength of EPS concrete. For a

30

1 mm 2.5 mm 6.3 mm 24%

21%

20

With PP fibre

1 mm 2.5 mm 6.3 mm 26%

15 22%

10

25%

0

30%

20%

5

26%

17.8


43%

55


178

3 2

0

10

20 30 40 Compressive strength: MPa

50

60

Figure 8. Variation of splitting tensile strength with compressive strength

given EPS bead, the increase was less pronounced with increasing EPS volume contents. It was also observed that the increase in strength with PP fibres was lower with an increase in EPS size for the same concrete density. For lightweight concrete with a matrix strength of 130 MPa and plastic density of 1800 kg/m3, the splitting tensile strength with PP fibres and 1?0 mm EPS beads increased by 44% in comparison with the corresponding EPS concrete without PP fibres, whereas for the samples with 2?5 and 6?3 mm EPS beads, the splitting tensile strength increased by 40 and 36%, respectively. It was observed during testing that the concrete with higher EPS volumes showed no abrupt split compared to normal 10 9 Splitting tensile strength: MPa


25

4

0

Without PP fibre

1 mm 2.5 mm 6.3 mm

×

5

1


.

1 mm 2.5 mm 6.3 mm

6 Splitting tensile strength: MPa


60

1 mm

With PP fibre

8 7

Without PP fibre

2.5 mm 6.3 mm

44%

40%

1 mm

2.5 mm 6.3 mm

36%

6

40%

5

38%

4

1 mm

2.5 mm 6.3 mm

36%

3

39%

2

37%

24%

1 0

1800


1000

Figure 9. Effect of PP fibre on the splitting tensile strength of EPS concrete with matrix of 130 MPa



Splitting tensile strength: MPa

6 5

Without PP fibre 1 mm

4 3 2

1 mm

2.5 mm 6.3 mm

1 mm 2.5 mm 6.3 mm

27% 18% 28%

1800

REFERENCES

26% 25%

1


ASTM (American Society for Testing and Materials) (1982) 40%

1000

Figure 10. Effect of PP fibre on the splitting tensile strength of EPS concrete with 50 MPa matrix

concrete and failed gradually, especially when comprising PP fibre.

4. (a)

(b)

(c)

(d)

(e)

This study was financially supported by the National Natural Science Foundation of China, Grant No. 50708059 and Key Laboratory of Advanced Civil Engineering Materials (Tongji University), Ministry of Education.

30%

22% 30%

0

With PP fibre

2.5 mm 6.3 mm

Acknowledgements

Conclusions For similar mix proportions, the EPS concrete with smaller size EPS aggregates showed higher compressive strengths. This was more pronounced in lower density concretes. The strength of EPS concrete increased with increasing concrete density and decreasing EPS volume fraction. This increase in strength was greater in high-strength matrices. For a given plastic density and EPS aggregate size, the normalised compressive strength increased with matrix strength. Therefore, incorporation of EPS beads in the concrete matrix may be more effective in obtaining highstrength concrete. For similar densities, PP fibres substantially improved the strength of EPS concrete. The increase in strength was greater in low-strength matrices. It was demonstrated that, for EPS concrete with a low-strength matrix, adding PP fibres to the concrete matrix improved the strength, potentially up to 24%. The 28-day compressive strengths of EPS concrete with PP fibres were up to 43% higher than the corresponding EPS concretes without PP fibres. The splitting tensile strength increased with the compressive strength. For similar mix proportions, PP fibres greatly improved the splitting tensile strength of EPS concrete. The 28-day splitting tensile strengths of EPS concrete with PP fibres were up to 44% higher than the corresponding EPS concretes without PP fibre.

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